src/error.md - rust-by-example - Git at Google

 # Error handling

 Error handling is the process of handling the possibility of failure. For
 example, failing to read a file and then continuing to use that *bad* input
 would clearly be problematic. Noticing and explicitly managing those errors
 saves the rest of the program from various pitfalls.

 There are various ways to deal with errors in Rust, which are described in the
 following subchapters. They all have more or less subtle differences and different
 use cases. As a rule of thumb:

 An explicit `panic` is mainly useful for tests and dealing with unrecoverable errors.
 For prototyping it can be useful, for example when dealing with functions that
 haven't been implemented yet, but in those cases the more descriptive `unimplemented`
 is better. In tests `panic` is a reasonable way to explicitly fail.

 The `Option` type is for when a value is optional or when the lack of a value is
 not an error condition. For example the parent of a directory - `/` and `C:` don't
 have one. When dealing with `Option`s, `unwrap` is fine for prototyping and cases
 where it's absolutely certain that there is guaranteed to be a value. However `expect`
 is more useful since it lets you specify an error message in case something goes
 wrong anyway.

 When there is a chance that things do go wrong and the caller has to deal with the
 problem, use `Result`. You can `unwrap` and `expect` them as well (please don't
 do that unless it's a test or quick prototype).

 For a more rigorous discussion of error handling, refer to the error
 handling section in the [official book][book].

 [book]: https://doc.rust-lang.org/book/ch09-00-error-handling.html
	# Error handling

	Error handling is the process of handling the possibility of failure. For
	example, failing to read a file and then continuing to use that bad input
	would clearly be problematic. Noticing and explicitly managing those errors
	saves the rest of the program from various pitfalls.

	There are various ways to deal with errors in Rust, which are described in the
	following subchapters. They all have more or less subtle differences and different
	use cases. As a rule of thumb:

	An explicit `panic` is mainly useful for tests and dealing with unrecoverable errors.
	For prototyping it can be useful, for example when dealing with functions that
	haven't been implemented yet, but in those cases the more descriptive `unimplemented`
	is better. In tests `panic` is a reasonable way to explicitly fail.

	The `Option` type is for when a value is optional or when the lack of a value is
	not an error condition. For example the parent of a directory - `/` and `C:` don't
	have one. When dealing with `Option`s, `unwrap` is fine for prototyping and cases
	where it's absolutely certain that there is guaranteed to be a value. However `expect`
	is more useful since it lets you specify an error message in case something goes
	wrong anyway.

	When there is a chance that things do go wrong and the caller has to deal with the
	problem, use `Result`. You can `unwrap` and `expect` them as well (please don't
	do that unless it's a test or quick prototype).

	For a more rigorous discussion of error handling, refer to the error
	handling section in the [official book][book].

	[book]: https://doc.rust-lang.org/book/ch09-00-error-handling.html